The present invention relates generally to the fabrication of magnetoresistive (MR) and inductive reproduce sensors or transducers for data storage applications, and more particularly, to an improved electrical lap guide (ELG) which controls the machining process such that the transducers are machined so a specified height.
During the fabrication of magnetic heads for use in magnetic data storage applications, an array of transducers and auxiliary circuits are fabricated on a common substrate in a deposition of metallic and non-metallic layers. The auxiliary circuits are sometimes referred to as electrical lap guides (ELGs). Patterning of the array of transducers and ELGs is accomplished using photolithography in combination with etching and lift-off processes. The finished array or wafer is then optically and electrically inspected and subsequently cut into smaller arrays, rows or bars. Next, individual rows or bars of transducers and ELGs are machined, at a surface which will eventually face the recording medium, to obtain a desired MR transducer height (sometimes referred to as the stripe height SH) or to obtain a desired inductive transducer height (sometimes referred to as the throat height TH).
During machining of a particular row of transducers and ELGs, the machined surface moves from a beginning position to a final position, while reducing the height of the transducers. The primary function of the ELG(s) is to control the machining process such that the desired transducer height is achieved. After a particular row of transducers is machined to the desired transducer height as controlled by the ELG(s), the rows or bars are cut or diced into individual recording heads or sliders. During this process, the ELG(s) can be destroyed if desired.
Typically, each ELG includes one or two resistors which are fabricated in the deposition of layers along with the transducers. A very simple ELG design has one resistor which is aligned with a transducer such that the machining process reduces the height of both the transducer and the resistor at the same time. The resistance of the machined resistor is monitored to determine when the desired height of the transducer has been achieved so that the machining process can be halted at this point. A more complex ELG design includes two resistors, one machined and the other a non-machined reference resistor. The resistance of the machined resistor is compared to the constant resistance of the reference resistor during the machining process. When the resistance of the machined resistor equals the resistance of the reference resistor, the machining process is halted, presumably at the point where the height of the machined resistor is approximately equal to the desired transducer height.
Numerous problems and difficulties are introduced with conventional ELG designs. One very common problem with conventional ELG designs is that they do not adequately account for errors introduced by the existence of mask or contact edge movement (also known as edge movement .DELTA.) caused by wafer processing steps. The edge movement phenomena caused by wafer processing results in the transducer and the resistors of the ELG being reduced or expanded in size as surfaces or edges of these elements move by a quantity .DELTA.. Thus, the actual lengths and heights of these elements will frequently be substantially different than the intended lengths and heights (i.e., than the mask lengths and heights). The dimension changes in the transducer and in the resistors of the ELG introduce errors in the machining process. For example, if the resistance of the reference resistor is dimensionally changed by edge movement, comparison of its resistance to the resistance of the machined resistor will result in the machining process being halted at the wrong time.
Failed attempts in the prior art to address the effects of edge movement on ELG performance made ELG performance wafer processing sensitive. Therefore, there is a need for an improved ELG design which both adequately compensates for the effects of wafer processing edge movement and which provides a method for determining the accuracy and/or trustworthiness of the ELG design.